1. Field of the Invention
The present invention relates to a solid-solution powder, a method for preparing the solid-solution powder, a cermet powder including the solid-solution powder, a method for preparing the cermet powder, a cermet using the cermet powder and a method to prepare the cermet, which are adapted to materials for high-speed cutting tools and die used in a machine industry such as manufacture of machine, an automotive industry and so on, in order to improve general mechanical properties, particularly toughness and hardness for the materials.
2. Description of the Related Art
For major cutting tools or wear-resistance tools utilized in metal cutting required for a machine industry, WC based hard alloys, various TiC or Ti(CN) based cermet alloys and other ceramic or high-speed steels, etc. are used.
A cermet means ceramic metal composite sinter. Usually, the cermet includes hard phase of TiC and Ti(CN) and binding phase of metal such as Ni, Co, Fe, etc., and an additive such as carbide, nitride, carbo-nitride, etc. of IVa, Va and VIa Group metals of the periodic table.
That is, usually, a cermet is prepared by mixing hard ceramic powders of WC, NbC, TaC, Mo2C, etc., in addition to TiC or Ti(CN), with metal powders of Co, Ni, etc., which is matrix phase for binding the ceramic powders, and sintering the mixture under a vacuum or hydrogen atmosphere.
Titanium carbide and titanium carbo-nitride are excellent hard materials with broad applications. As titanium carbide has a high hardness (Vicker's=3200 kg/mm2), high melting points (3260° C.), high chemical and thermal stability, high wear-resistance and high solvency for other carbides, it has been used for high-speed cutting tools in substitution of WC—Co alloy. However, in the TiC—Ni cermet system, coarsening of TiC grains results in poor mechanical properties. Further, in case of preparing a cermet using TiC, upon sintered, binding phase metal of Ni is used as a liquid metal, so that a wetting angle comes to be large in comparison with that of a combination of WC—Co and rapid grain growth of TiC comes to occur, which cause the problem of reducing a toughness of the cermet.
Nevertheless, in 1956, Ford Motor Company mass-fabricated TiC—Mo2C—Ni cermet. Although the toughness of the cermet was not largely improved, the cermet had been used in semi-finishing and finishing as material for high hardness tools for precise machining operations.
In the 1960's and 1970's, to improve the toughness that was a great weakness of the TiC—Ni cermet system, there had been an attempt to add various kinds of elements thereto, which, however, could not have attained tangible results.
On the way, in the 1970's, performed was adding TiN to TiC in order to form Ti(C,N) of a more stable thermodynamic phase, which could improve toughness in a certain degree.
That is, since Ti(C,N) had a micro fine structure in comparison with TiC, toughness thereof had been improved, in addition to a chemical stability and a mechanical shock resistance.
Meanwhile, to improve toughness, various additive carbides such as WC, Mo2C, TaC, NbC, etc. have been used, and even now products in the form of Ti(C,N)-M1C-M2C- . . . —Ni/Co are commercializing.
When adapting the additive carbides for the improvement of toughness, a general microstructure of TiC based or Ti(C,N) based cermet sinter is observed as a core/rim structure of hard phase, around which Ni, Co, etc. of binding phase surround.
The core of the structure is undissolved TiC or Ti(C,N) in liquefied metal binder (Ni, Co and so on) during sintering, the core having a structure with high hardness.
On the contrary, a structure of rim surrounding the core is a solid-solution of TiC or Ti(CN), which is the component of the core, and the carbides, which are the additives [the solid-solution is expressed as (Ti, M1, M2 . . . )(C,N)].
The structure of rim has high toughness rather than hardness. Therefore, in order to resolve the fatal weakness of toughness that simple cermet such as TiC or Ti(C,N)—Ni has, the structure of rim has been provided in the cermet.
However, the cermet having such core/rim structure still has a problem in that the cermet has toughness lower than that of WC—Co hard alloy, so that the cermet cannot yet replace WC—Co completely.
Further, the strain developed at the interface between core and rim phases exerts a negative effect on the properties, facilitating crack propagation through the interface during machining. Thus, there have been enormous efforts to produce homogeneous solid-solutions of single phase without core/rim structure in order to secure the application area of the cermet as broad as WC—Co. However, many industrial attempts targeting this homogeneity have failed to provide it.